Unity Test 單元測試

Principle 

is to isolate each part of the program and show that the individual parts are correct. A unit test provides a strict, written contract that the piece of code must satisfy. As a result, it affords several benefits.

Ideally, each test case is independent from the others. Substitutes such as method stubs, mock objects, fakes, and test harnesses can be used to assist testing a module in isolation

Benefits

• Find problems early
• TDD helps you to realise when to stop coding. Your tests give you confidence that you've done enough for now and can stop tweaking and move on to the next thing.
• Unit Tests help you really understand the design of the code you are working on. Instead of writing code to do something, you are starting by outlining all the conditions you are subjecting the code to and what outputs you'd expect from that.
• Contrary to popular belief unit testing does not mean writing twice as much code, or coding slower. It's faster and more robust than coding without tests once you've got the hang of it.
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limitation

• 測試不可能發現所有的程式錯誤，單元測試也不例外。
• 單元測試只測試程式單元自身的功能。因此，它不能發現整合錯誤、效能問題、或者其他系統級別的問題。
• 單元測試只能表明測到的問題，不能表明不存在未測試到的錯誤。